For a number of years, one of the more popular commercial ways of producing chlorine and caustic by electrolysis has been by the use of electrolysis cells in which arrays of rectangular prism-shaped parallel anodes were made of solid, relatively thick graphite, which anodes were between arrays of rectangular prism shaped, hollow cathode pockets. These cathode pockets were usually coated with diaphragms such as asbestos.
In recent years much research has gone into developing improvements in this type of cell in general, and in improvements in the anodes in particular. A number of types of metal anodes have been developed which could tolerate the highly corrosive environment within the anolyte compartment of these cells as well or better than the graphite blocks or blades. These metals are the valve metals such as titanium and tantalum. Several types of anode made from these metals have been designed to replace the relatively thick graphite blocks. In many instances where it was desired to use these metal anodes, it was, and often still is, also desirable to retain as much of the existing cells as possible. That is, only replacing the graphite anodes with the new metal anodes. The working faces of these new anodes were made of the valve metals and coated with a catalyst such as ruthenium oxide and cobalt oxide.
Generally these valve metals were and are much too expensive to merely replace the thick blocks of graphite with blocks of these metals of the same thickness. However, one single thin metal sheet could not be inserted as an anode between the cathode pockets and have a sufficiently narrow gap between the anodes and cathodes for satisfactory commercial operation. In commercial chlor-alkali electrolysis production cells, this gap width is very important. The wider the gap, the more waste these is of electrical power due to the increased electrical resistance in the anolyte. Yet if this anode-to-cathode gap is too small, there results such poor circulation of the brine in the gap that there is an unacceptable increase of undesirable, diaphragm destroying chemicals produced in this too narrow gap. Further during cell assembly a wide anode-cathode gap was, and is, desired to prevent the anodes from damaging the diaphragms, such as by scraping holes in them, as the array of anodes are slipped between the diaphragm-coated cathode pockets.
Hence adjustable anode assemblies have been made from these valve metals that could be slid between the cathodes. These assemblies generally involve using several parts with extensive complicated welding or other attaching means for these parts. See U.S. Pat. Nos. 3,674,676 (Fogelman) and 3,941,676 (Pulver).
Moreover, another undesirable feature has been observed. Each cathode pocket in a row of cathode pockets in a cell should have an anode assembly on each side of it, including the terminal cathode pockets of that row. This means, for example, that if a row contains twenty (20) cathode pockets, then twenty-one (21) of the anode assemblies would be required. Without an anode assembly on each side of the terminal cathode pockets, these terminal cathodes would be quickly corroded.
Hence, it would be advantageous to have an electrode assembly utilizing a dimensionally stable anode which is simple to construct, and is less expensive than presently available. Further, it would be advantageous to have an electrode assembly which provides a predetermined anode-cathode gap width which also protects the diaphragm, or other selective barrier, from damage during cell assembly. In addition it would be advantageous to have an electrode assembly which required no more anode assemblies than cathode assemblies in a row of interleaved anodes and cathode pocket usually found in an electrolysis cell, particularly a chlorine-caustic electrolytic cell. These and other advantages are provided by the present invention.